An internal combustion engine usually has cylinders each defining a combustion chamber, in which fuel and a combustion agent are introduced for the combustion of the mixture. The engine allows the energy released by this combustion to be transformed into mechanical energy.
In such an engine it is known to provide each cylinder with a sensor for measuring the pressure prevailing in the combustion chamber of said cylinder, the set of sensors being connected to a processing unit. This processing unit is generally provided, as is known, in the form of a computer referred to as an electronic control unit (engine control unit or ECU), which makes it possible to adjust the control parameters of the engine of the vehicle, such as the injection of fuel into the cylinder or the post-treatment of polluting emissions.
A pressure measurement sensor, as is known, uses the variations of electrical charge of a sensitive piezoelectric element to provide, in a relative manner, an indication of the pressure prevailing in the cylinder. Such a sensor, at the output, provides a voltage signal representative of these pressure variations. An example of a signal provided by a pressure measurement sensor in a cylinder is illustrated in FIG. 1. This voltage signal S_in varies in terms of frequency and amplitude and alternates between substantially linear phases and voltage peaks, referred to as “main peaks”, representing the peaks of the pressure prevailing inside the combustion chamber of the cylinder during phases of compression and combustion of the gases.
The linear phases progress substantially in accordance with a straight line of zero, positive, or negative gradient. The non-zero values of this gradient result from noises and offsets, caused in particular by phenomena of pyroelectricity and/or vibrations experienced by the sensor. In particular the heating of the ceramic by the heat released by the combustion of the gases in the cylinder may create a current generating an additional electrical charge in the sensor, referred to as “pyroelectricity”.
More precisely, FIG. 2 shows a detailed example of a noised voltage signal S_in of a pressure measurement sensor, said signal progressing over time t in accordance with a straight line of positive gradient A. As explained above, the signal S_in may be assimilated to an alternation between “plateau” phases SP1, SP2, SP3, during which the voltage differs from a reference value VREF and progresses over time on average in accordance with a straight line, in this example with a positive gradient, and voltage peaks P1, P2, P3, which are representative of combustion pressure peaks.
The signal S_in generally has weak variations VAR representative of noise. In addition, as illustrated in FIG. 10B, a main peak may have variations at the apex thereof taking the form of a double-peak PIA, P1B. This double-peak PIA, P1B is representative of the combustion noises of the gases in the cylinder when the pressure reaches maximum values in the combustion chamber. In addition, pressure peaks of low amplitude, referred to as “secondary peaks” PS (with reference to FIG. 8), may be generated by valve noises and may reach amplitudes close to main peaks of low amplitude (i.e. at low speed of the engine of the vehicle).
The processing unit processes the voltage signal S_in at the output of each sensor so as to make it usable by the electronic control unit ECU. This processing includes a rectification of the signal so as to compensate for the offset thereof. With this objective it is necessary to detect the pressure peaks in order to compensate the signal solely during the plateau phases and so as to thus obtain a signal having, in alternation, original main peaks and plateaus of zero gradient. For this purpose the processing unit, as is known, comprises a peak detection sub-unit and a compensation sub-unit aiming to compensate for the gradient of the signal. The processing unit is generally provided in the form of a dedicated integrated circuit of the “ASIC” type (application specific integrated circuit), connected to the pressure measurement sensor.
A method known from the prior art, based on “Kalman” filters, is based on a method for the recursive correction of an error between the output signal and the prediction thereof attenuated by a gain. The prediction of the signal is then calculated on the basis of the filtered and corrected signal at the moment of prior acquisition. More particularly and in accordance with document FR 2 938 645 A1, it is known to use two Kalman filters: a “fast” Kalman filter, i.e. having gradient and constant gains with high values for the points belonging to the pressure peaks, and a “slow” Kalman filter, i.e. having gradient and constant gains with low values for determining the offset of the signal, i.e. the offset during the plateau phases. This method makes it possible to correct the signal point by point on the basis of whether or not said point belongs to the plateaus.
Such a method, however, has a number of disadvantages. Firstly, each point of the signal is processed by a complex calculation using a Kalman filter, which is time-consuming and uses a significant amount of the memory of the ASIC circuit. Then, the method is difficult to calibrate since it has four variables to be parameterized: a pair comprising a gradient gain and a constant gain for the fast Kalman filter and another pair comprising a gradient gain and a constant gain for the slow Kalman filter. In addition, as illustrated in FIG. 10B, the oscillations of the signal at the apex of the main peaks at the start of combustion lead the Kalman filter to detect a number of peaks P1A, P1B and to improperly compensate for the signal therebetween. Still with reference to FIG. 10B, the peak detection signal 200 then performs an erroneous double detection Y1, Y2, making the compensated signal inaccurate, which is detrimental to the adjustment of the operating parameters of the engine. Likewise, the peaks representing valve noises, or what are known as secondary peaks PS (with reference to FIG. 8), may be confused by the Kalman filter with low-value main pressure peaks (for example the peak P6 in FIG. 8), which leads the Kalman filter to improperly compensate for the signal therebetween, thus rendering the compensated signal inaccurate, which is also detrimental to the adjustment of the operating parameters of the engine.
The object of the present invention is to overcome these disadvantages by proposing a simple and reliable solution for detecting, with accuracy, the main pressure peaks of the gases in a cylinder of an internal combustion engine of a vehicle so as to provide a compensated signal that can be used effectively in order to manage the parameters of the engine.